Direct versus indirect loading of orthodontic miniscrew implants-an FEM analysis.

OBJECTIVE: The mesialization of molars in the lower jaw represents a particularly demanding scenario for the quality of orthodontic anchorage. The use of miniscrew implants has proven particularly effective; whereby, these orthodontic implants are either directly loaded (direct anchorage) or employed indirectly to stabilize a dental anchorage block (indirect anchorage). The objective of this study was to analyze the biomechanical differences between direct and indirect anchorage and their effects on the primary stability of the miniscrew implants. MATERIALS AND METHODS: For this purpose, several computer-aided design/computer-aided manufacturing (CAD-CAM)-models were prepared from the CT data of a 21-year-old patient, and these were combined with virtually constructed models of brackets, arches, and miniscrew implants. Based on this, four finite element method (FEM) models were generated by three-dimensional meshing. Material properties, boundary conditions, and the quality of applied forces (direction and magnitude) were defined. After solving the FEM equations, strain values were recorded at predefined measuring points. The calculations made using the FEM models with direct and indirect anchorage were statistically evaluated. RESULTS: The loading of the compact bone in the proximity of the miniscrew was clearly greater with direct than it was with indirect anchorage. The more anchor teeth were integrated into the anchoring block with indirect anchorage, the smaller was the peri-implant loading of the bone. CONCLUSIONS: Indirect miniscrew anchorage is a reliable possibility to reduce the peri-implant loading of the bone and to reduce the risk of losing the miniscrew. The more teeth are integrated into the anchoring block, the higher is this protective effect. CLINICAL RELEVANCE: In clinical situations requiring major orthodontic forces, it is better to choose an indirect anchorage in order to minimize the risk of losing the miniscrew.

Orthodontic tooth movement in the mixed dentition. Histological study of a human specimen.

MATERIAL AND METHOD: We present a retrospective analysis of periodontal tissue reactions and clinically relevant phases of permanent tooth eruption and deciduous tooth resorption after half a year of orthodontic tooth movement in the upper and lower jaw of a deceased male (age 9 years 3 months). Specimens of the horizontal plane (lower jaw) and sagittal plane (upper jaw) were prepared by the ground microsection technique without prior decalcification. RESULTS: Histologically, reactions in the periodontal ligament presented as characteristic appositional/resorptive metaplastic processes in the areas of tension and pressure, with side effects such as root resorption and periodontal necrosis being only minor. In the upper jaw, an erupting permanent canine was closely associated with the tooth germ of the first premolar. Resorptive follicle activity had resulted in extensive erosion of the interradicular bone and root resorption in the area of the first premolars. CONCLUSION: These findings suggest that it might prove useful to take critical topographic findings as parameters for differential therapeutic decisions. Follicle-driven deciduous tooth resorption presenting partly as resorption lacunae and partly with linear characteristics was accompanied by resorptive/appositional remodeling of the alveolar socket as well as regressive changes in the supracrestal fibers of the marginal gingiva.

Effects of orthodontic bands on marginal periodontal tissues. A histologic study on two human specimens.

Eight banded teeth on two human specimens (9 years, male; 19 years, female) were analyzed regarding the fit of the orthodontic bands and periodontal reactions. Five teeth (three molars, two premolars) were evaluated histologically in the horizontal plane and three (one molar, two premolars) in the sagittal plane using the micro-section method according to Donath. The fit of the bands varied in occluso-apical direction. The mean of marginal gaps was x = 0.23 mm in the occlusal, x = 0.03 mm in the equatorial, and x = 0.28 mm in the cervical area. In the equatorial area the thin cement layer was largely homogeneous, whereas porosities and microfissures were found predominantly in thicker cement layers. 85% of the occlusal and cervical band margins revealed cement defects and/or erosions which were colonized by felted, partially densely compacted microbial plaque. With regard to the periodontal effects, the signs of inflammation in the buccolingual gingival areas were markedly less severe due to the supramarginal position of the band margins. The interdental gingiva of all teeth presented the histological pattern of an established gingival lesion. Leukocyte infiltration and inflammatory exudation in the area of the transseptal fibers were exceptionally pronounced in one lower molar (band exposure time: 6 months). At this site the connective tissue attachment close to the cementoenamel junction was severely damaged on the mesial surface and the pocket epithelium proliferated towards the apex, meaning progression from established gingivitis to an initial periodontal lesion. The histologic findings on these human periodontal tissues confirm that the application and hygiene control of orthodontic bands have to be performed with great care to avoid permanent periodontal destruction.

Functional appliance therapy with the Bionator.

Since the early 20th century, functional appliance therapy has been a significant part of orthodontic treatment, especially in Europe, where functional appliances have been used to treat many malocclusions, including some skeletal discrepancies. Although the success of functional appliance therapy as reported in numerous short-term studies from 1930 to 1975 led to an euphoric acceptance of this method, the few long-term studies, especially those comparing treated with untreated homogeneous control groups, indicated that the specific skeletal and dentoalveolar effects depended on the individual growth period and pattern of the patient. In this article, a specific functional appliance, the Bionator, is presented. Long-term follow-up studies provide indications for its use. At the present time, functional orthopedic appliance therapy has a more limited but well-defined place in our therapeutic approach. The type and character of the malocclusion determines the indications and contraindications of the functional appliance. Scientific and clinical experience has shown the importance of a differential diagnosis for each patient, which integrates etiology and morphogenesis in the individual treatment objectives for special skeletal, dentoalveolar, and functional regions. Individualization in the construction of the appliance, taking the above-mentioned factors into consideration, is essential for optimal clinical results.

Endosseous dental implants in orthodontic therapy.

This paper presents cases in which endosseous titanium implants are used in orthodontic treatment as an alternative method of providing anchorage, as well as solving prosthodontic problems, and shows that such an approach can be successful.